1. Field of the Invention
The present invention relates to a differential case for a vehicle and a differential device for a vehicle, and more particularly relates to a differential case for a vehicle and a differential device for a vehicle having plural pinion gear supporting portion supporting slidably plural pinion gears being a shaft-less type.
2. Description of the Related Art
It is well known for a prior differential device for a vehicle to provide a pair of shaft-less pinion gears as disclosed in a published patent document; Tokkai 2006-46642.
The differential device for the vehicle comprises a pair of pinion gears, a pair of side gears engaging with the pair of pinion gears, a differential case rotatably mounting the pair of pinion gears and the pair of side gears.
The pair of pinion gears has a gear peripheral portion as a supported portion over all around periphery and a gear engaging portion engaging with the pair of side gears and the pair of pinion gears are disposed in the differential case on an axis perpendicular to a rotational axis of the differential case. An inside face of the pair of side gears is connected with right and left tire shafts in a spline engagement. In the differential case is mounted a pinion gear penetrating hole having a first pinion gear supporting face to support slidably the gear peripheral portion of the pair of pinion gears. Around of an inner opening of the pinion gear penetrating hole is mounted an extending portion having a second pinion gear supporting portion to support slidably a part of the gear engaging portion of the pinion gears.
Based on the above-mentioned construction, when torque from an engine is input into the differential case through a driving pinion and a ring gear, the differential case is rotated around the rotational axis. At the rotation of the differential case, the rotational force is transmitted to the pair of pinion gears and the pair of side gears through the pair of pinion gears. Therefore, the torque is distributed and transmitted differentially to right and left tire shafts according to a running condition of the vehicle since the pair of side gears engages with right and left tire shafts in the spline engagement.
In running of the vehicle, where the vehicle turns in a stage to transmit large torque to the differential case, the pinion gears slide in a stage to be pushed on the first pinion gear supporting face of the pinion gear penetrating hole and the second pinion gear supporting face of the extending portion. At this moment, a part of frictional heat generating between the sliding surface of the pinion gear and the first pinion gear supporting face of the pinion gear penetrating hole and also between the sliding surface of the pinion gear and the second pinion gear supporting face of the extending portion is cooled by lubrication oil supplied to a clearance between the sliding surface of the pinion gear and the first pinion gear supporting face of the pinion gear penetrating hole and also between the sliding surface of the pinion gear and the second pinion gear supporting face of the extending portion. Therefore, the well known differential device for the vehicle disclosed in the published patent document lubricates between the sliding surface of the pinion gear and the first pinion gear supporting face of the pinion gear penetrating hole and also between the sliding surface of the pinion gear and the second pinion gear supporting face of the extending portion and it discharge frictional heat by the way of movement of lubrication oil by the rotation of the differential case.
However, in the well known differential device for the vehicle disclosed in the published patent document, there is the problem that lubrication oil is not supplied sufficiently around the gear peripheral portion as the supporting portion of the pinion gear to cause the gear peripheral portion of the pinion gears to be bonded in burn. This is happened more in large diameter of the pinion gears.